"As you know, we experienced a temporary issue in an internal systems update that unfortunately had a flaw in it. We identified the issue and returned to business as usual," United Bank said in a statement Friday.

The bank has not specified the number of accounts affected. A spokesperson for the Connecticut Department of Banking said United Bank was not hacked; rather, it had planned an "IT change" that ran into trouble when it went live Wednesday.

Then, out of an abundance of caution, United Bank took the online banking system down to protect customer data, according to the Department of Banking.

The department said there is not "any evidence of any lingering impact on customers" and clarified that affected customers could still go their branches for services during the outage and had limited usage of the ATM network as well.